Abstract. Using laser absorption spectrometry for the measurement of stable isotopes of atmospheric CO₂ instead of the traditional Isotope Ratio Mass Spectrometry (IRMS) method decreases sample preparation time significantly, and uncertainties in the measurement accuracy due to CO₂ extraction and isobaric interferences are avoided. In this study we present the measurement performance of a new dual-laser instrument developed for the simultaneous measurement of the δ¹³C, δ¹⁸O and δ¹⁷O of atmospheric CO₂ in discrete air samples, referred to as the Stable Isotopes of CO₂ Absorption Spectrometer (SICAS). We compare two different calibration methods: the ratio method (RM) based on measured isotope ratio and a CO₂ mole fraction dependency correction (CMFD), and the isotopologue method (IM) based on measured isotopologue abundances. Calibration with the RM and IM is based on three different assigned whole air references calibrated on the VPBD scale. An additional quality control tank (QC) is included in both methods to follow long-term instrument performance. Measurements of the QC tank show that best performance is achieved with the RM for both the δ¹³C and δ¹⁸O measurements with mean residuals of 0.007 ‰ and 0.016 ‰ and mean standard errors of 0.009 ‰ and 0.008 ‰ respectively, during periods of optimal measurement conditions. The δ¹⁷O standard error in the same measurement period is 0.013 ‰. In addition, intercomparing a total of 14 different flask samples covering a CO₂ mole fraction range of 344–439 ppm with the Max Planck Institute for Biogeochemistry shows a mean residual of 0.002 ‰ and a standard deviation of 0.063 ‰ for δ¹³C, using the RM. The δ¹⁸O could not be compared due to depletion of the δ¹⁸O signal in our sample flasks because of too long storage times. Finally, we evaluated the potential of our Δ¹⁷O measurements as a tracer for Gross Primary Production (GPP) by vegetation through photosynthesis. Here, a measurement precision of 17O signal. So far, a mean standard error of 0.016 ‰ was achieved for Δ¹⁷O measurements of our QC tank using the RM. Improvements in our measurement procedure, spectral fit and δ¹⁷O calibration are due to reach the required precision.

中文翻译：

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δ的同时测量¹³ C，δ ¹⁸ O和δ ¹⁷大气CO的O- ₂ -的双激光吸收光谱仪的性能评价

摘要。使用激光吸收光谱法测量大气中CO ₂的稳定同位素，而不是传统的同位素比率质谱法（IRMS），可显着减少样品制备时间，并且避免了由于CO ₂提取和等压干扰造成的测量精度不确定性。在这项研究中，我们提出了δ的同时测量开发了一种新的双激光仪器的测量性能¹³ C，δ ¹⁸ O和δ ¹⁷ ö大气CO的₂离散空气样本中，被称为CO的稳定同位素₂吸收光谱仪（SICAS）。我们比较了两种不同的校准方法：基于测得的同位素比率和CO ₂摩尔分数依赖性修正（CMFD）的比率法（RM）和基于测得的同位素同位素丰度的同位素同位素法（IM）。RM和IM的校准基于在VPBD刻度上校准的三个不同的分配的整体空气参考。两种方法都包括一个额外的质量控制罐（QC），以遵循长期的仪器性能。的QC罐显示测量其最佳性能与RM两者的δ实现¹³ C和δ ¹⁸在最佳测量条件期间，O测量的平均残差分别为0.007‰和0.016‰，平均标准误为0.009‰和0.008‰。的δ ¹⁷在同一测量时期O标准误差为0.013‰。此外，相互比较总共覆盖CO 14个不同瓶样品₂ 344-439 ppm的与马普摩尔分数范围为生物地球化学示出了平均残余0.002‰和0.063‰为δ的标准偏差¹³ C，使用RM。该δ ¹⁸ Ø无法相比，由于δ消耗¹⁸因存放过久的时候，我们的样本瓶输出信号。最后，我们评估了我们Δ的潜力¹⁷O测量值作为植被通过光合作用的总初级生产量（GPP）的示踪剂。此处，测量精度为17O信号。到目前为止，对于Δ达到0.016‰，平均标准误差^17次使用RM我们的QC罐Ø测量。在我们的测量程序，光谱配合和δ改进¹⁷ ö校准是由于达到所要求的精度。